Methods and systems for controlling a drive train of a motor vehicle are known and are shown, for example, in the lower portion of FIG. 1. Here, the motor 15 is connected via a main clutch or converter-bridge clutch 16 and a transmission 17 to the drive wheels 18 of the vehicle. Here, it can also be provided that the main clutch 16 is mounted downstream of the transmission 17. The transmission 17 is a so-called CVT transmission which is continuously variable with respect to its transmission ratio. The motor 15, the main clutch 16 as well as the CVT transmission 17 are controlled by the corresponding controls 12, 13 and 14. Furthermore, at least the detection of the motor rpm Nmot and the transmission input rpm Nge is provided. In such CVT transmissions, the transmission ratio can be adjusted over a large range. The driver can, in general, select between the position N (neutral), the position P (park position) and the position D (drive stage) via a transmission selector. If the driver selects the position N (neutral), the main clutch 16 is opened and the force flow is essentially interrupted in the drive train. In the neutral position, a slight force flow can still be provided for safety.
If the main clutch 16 is closed while the vehicle is moving in that the driver switches from the position N (neutral) into the position D (drive stage), then a severe jolt can occur in the drive train of the vehicle because the main clutch 16 must again be closed and the transmission input rpm Nge and/or the clutch output rpm are not adapted to the motor rpm Nmot. Because of this instantaneous jolt, the vehicle can enter into an unstable driving condition under some circumstances.
Up to now, in general, the motor torque is not influenced when opening the main clutch of the transmission. Depending upon the position of the accelerator pedal actuated by the driver, a motor rpm adjusts which lies between the motor idle rpm and the breakaway rpm (maximum motor rpm). In general, the transmission control 14 then adjusts the transmission 17 in a direction of lower transmission ratios (low) or toward a transmission ratio which is determined from the driving program stored in the transmission control 14. The driving program is determined by means of the accelerator pedal position and the driving speed of the vehicle. When again engaging the main clutch 16, the jolt results from the typically high difference of the rpm at the two ends of the main clutch 16 and is therefore unavoidable in such systems.
In addition to the above-mentioned continuously variable transmissions (CVT transmissions), stepped transmissions are also known whose transmission ratio can be adjusted in a stepwise manner. Stepped transmissions are known as conventional fully automatic transmissions and automated shift transmissions.
It is an object of the invention to provide a jolt-free transition when closing the main clutch.
The method of the invention is for controlling the drive train of a motor vehicle. The drive train includes at least a motor having a motor output rpm, a transmission and a main clutch, the drive train having at least first and second operating states (D, N) selectable by the driver of the vehicle, the first operating state (D) being provided during normal driving operation and, during the second operating state (N), the force flow in the drive train being essentially interrupted. The method includes the steps of: detecting a motor rpm quantity (Nmot), which is representative of the motor output rpm, and detecting a transmission input rpm quantity (Nge), which is representative of the transmission input rpm; and, in the second operating state (N), adjusting the motor rpm quantity (Nmot) to the transmission input rpm quantity (Nge).
As mentioned, the invention proceeds from a method and an arrangement for controlling a drive train of a motor vehicle. The following are provided in the drive train: a motor, a transmission and a main clutch and the transmission is especially a transmission which is continuously variable with respect to its transmission ratio. The driver of the vehicle can select between different operating states of the drive train. In a first operating state, the normal driving operation is provided; whereas, in a second operating state, the force flow in the drive train is essentially interrupted. In addition to a complete interruption of the drive flow via a complete opening of the clutch, a low force flow can be provided in the second operating state (neutral position) for the reason of safety. Furthermore, the motor output rpm as well as the transmission input rpm are detected by corresponding rpm quantities.
The essence of the invention is that, in the second operating state, wherein the force flow in the drive train is essentially interrupted, the motor rpm is adjusted to the transmission input rpm. This affords the advantage that no large rpm differences are present at the clutch input and the clutch output when closing the main clutch. The closing of the main clutch can therefore take place essentially jolt free.
In an advantageous embodiment of the invention, it is provided to adjust the motor rpm to the transmission input rpm in such a manner that a desired value is formed in dependence upon the transmission input rpm. The motor rpm is then controlled to this desired value.
According to another feature of the invention, the vehicle longitudinal speed is detected by a corresponding quantity. The adjustment of the motor rpm to the transmission input rpm is then dependent upon whether the driving speed is greater or less than a pregiven threshold value. Here, it is especially provided that the adjustment of the motor rpm to the transmission input rpm takes place when the driving speed is greater than the threshold value. In this configuration of the invention, it is also provided that, in addition to the second operating state (no or only a slight force flow in the drive train, main clutch open or essentially open), the driving speed continues to be considered.
It can be especially provided that, when the driving speed is less than the threshold value, the motor rpm is adjusted in dependence upon the position of the accelerator pedal actuated by the driver. At low driving speeds (for example, less than 25 km/h), the driver must adjust a motor desired rpm with the accelerator pedal as when the vehicle is at standstill. In this low driving speed range, the transmission is adjusted in an advantageous manner only in a limited range so that the vehicle still exhibits an adequate acceleration capability when the gear is again engaged or when the main clutch is closed.
In a further advantageous embodiment of the invention, it is provided that the motor rpm quantity is limited to pregiven values when the driving speed is greater than the threshold value. This feature relates to the state which can occur at high driving speeds during opening of the main clutch. In this case, the motor rpm to be adjusted may not exceed the maximum motor rpm.
As already mentioned above, the main clutch is essentially opened in reaction to a change from the first operating state to the second operating state. If the change takes place from the second operating state to the first operating state (in general, this is effected by the driver), then the main clutch is actuated in the sense of a closing. Here, it can be especially provided that the closing takes place with maximum clutch adjusting speed. In this way, one achieves a very rapid restoration of the force flow without a noticeable jolt being felt in the drive train because the clutch input and clutch output speeds are essentially the same.